PROJECT SUMMARY/ABSTRACT Fascioliasis is a global food-borne trematode infection targeted by WHO as an important neglected tropical disease due to its high impact in human and livestock populations around the world. Triclabendazole is the only drug recommended for treatment, but drug resistance is widespread in livestock and is an emerging problem among infected humans. The mechanisms of triclabendazole resistance are not known and there are no reliable markers that predict the susceptibility phenotype among infected subjects. Targeted evaluation of specific candidate genes has yielded inconsistent results, likely due to the complexity of genotype-phenotype relationships. The current proposal will use a genome-wide association approach to identify genetic variants that are associated with triclabendazole resistance by analyzing the genomes of a large number of Fasciola parasites infecting animals, including susceptible and triclabendazole-resistant isolates. The resistance-associated loci will be validated using human-infecting parasites because we hypothesize that, due to the zoonotic nature of F. hepatica, the variants contributing to resistance in animal and human hosts are conserved. Lastly, the current grant will evaluate the transcriptional response of different stages of Fasciola exposed to various doses of triclabendazole to uncover the mechanisms that induce resistance to triclabendazole. This is a well-rounded proposal that upon completion will provide a mechanistic understanding of the biological processes that determine the triclabendazole resistance phenotype and a set of reliable genetic markers that distinguish between resistant and susceptible Fasciola parasites. In the long term, the results of this study may allow the creation of diagnostic tools for early identification of TCBZ-R, to direct treatment of infected subjects, and provide guidance for stewardship and control strategies. Identifying and restoring altered pathways may also help overcome resistance and make TCBZ effective again. In addition, we will set-up of a model to study other trematode parasites with complex lifecycles.